Merge pull request #5605 from unisonweb/25-03-04-merge-bugfix

bugfix: merge name-pick bug

Author: aryairani

unison-core/src/Unison/Names.hs

@@ -233,9 +233,9 @@ preferring :: Names -> Names -> Names
 preferring xs ys =
   Names (preferring1 xs.terms ys.terms) (preferring1 xs.types ys.types)
   where
-    preferring1 :: (Ord a, Ord b) => Relation a b -> Relation a b -> Relation a b
+    preferring1 :: (Ord ref) => Relation Name ref -> Relation Name ref -> Relation Name ref
     preferring1 =
-      Relation.unionRangeWith (\_ x _ -> x)
+      Relation.unionRangeWith (\_ref xs _ys -> xs)
 
 -- | TODO: get this from database. For now it's a constant.
 numHashChars :: Int

unison-merge/src/Unison/Merge/Mergeblob3.hs

@@ -374,7 +374,12 @@ makePrettyPrintEnv names libdepsNames lcaLibdeps =
   PPED.makePPED
     ( PPE.namer
         ( Names.preferring
-            (Names.preferring names.alice names.bob <> libdepsNames)
+            -- Here it might be slightly more comfortable to Alice if we prefer her names and _her_ libdeps, not the
+            -- combined Alice+Bob libdep, because that might bring in a Bob name that Alice isn't yet familiar with
+            -- (even though it will be in her merge result at the end). However, that would require a bit of simple
+            -- refactoring (just need to delay the combining of libdeps until at least here), and doesn't seem worth it
+            -- over this quick fix of just "prefer Alice + any libdep name over names that only Bob's project has".
+            (Names.preferring (names.alice <> libdepsNames) names.bob)
             (names.lca <> lcaLibdeps)
         )
     )

unison-src/transcripts/idempotent/fix-5604.md

@@ -0,0 +1,135 @@
+``` ucm
+scratch/main> builtins.mergeio lib.builtin
+
+  Done.
+```
+
+The situation:
+
+  - topic has two names for a thing (foo and lib.bar)
+  - main delete one alias (foo, leaving lib.bar)
+  - When merging topic into main, for some reason we render topic's stuff that depends on that thing as referring to
+    `foo`, which main deleted\!
+
+``` ucm
+scratch/main> alias.type lib.builtin.Nat MyNat
+
+  Done.
+```
+
+``` unison
+foo : Nat
+foo = 17
+```
+
+``` ucm :added-by-ucm
+  Loading changes detected in scratch.u.
+
+  I found and typechecked these definitions in scratch.u. If you
+  do an `add` or `update`, here's how your codebase would
+  change:
+
+    ⍟ These new definitions are ok to `add`:
+    
+      foo : MyNat
+```
+
+``` ucm
+scratch/main> add
+
+  ⍟ I've added these definitions:
+
+    foo : MyNat
+
+scratch/main> branch topic
+
+  Done. I've created the topic branch based off of main.
+
+  Tip: To merge your work back into the main branch, first
+       `switch /main` then `merge /topic`.
+
+scratch/topic> switch /main
+
+scratch/main> delete.type MyNat
+
+  Done.
+```
+
+``` unison
+foo : Nat
+foo = 18
+```
+
+``` ucm :added-by-ucm
+  Loading changes detected in scratch.u.
+
+  I found and typechecked these definitions in scratch.u. If you
+  do an `add` or `update`, here's how your codebase would
+  change:
+
+    ⍟ These names already exist. You can `update` them to your
+      new definition:
+    
+      foo : Nat
+```
+
+``` ucm
+scratch/main> update
+
+  Okay, I'm searching the branch for code that needs to be
+  updated...
+
+  Done.
+
+scratch/main> switch /topic
+```
+
+``` unison
+bar : MyNat
+bar = foo + foo
+```
+
+``` ucm :added-by-ucm
+  Loading changes detected in scratch.u.
+
+  I found and typechecked these definitions in scratch.u. If you
+  do an `add` or `update`, here's how your codebase would
+  change:
+
+    ⍟ These new definitions are ok to `add`:
+    
+      bar : MyNat
+```
+
+``` ucm
+scratch/topic> add
+
+  ⍟ I've added these definitions:
+
+    bar : MyNat
+
+scratch/topic> switch /main
+```
+
+This merge used to fail because it rendered `bar` using the deleted name `MyNat` (rather than the still-existing name
+`Nat`).
+
+``` ucm
+scratch/main> merge /topic
+
+  Loading branches...
+
+  Loading definitions...
+
+  Computing diffs...
+
+  Loading dependents of changes...
+
+  Loading and merging library dependencies...
+
+  Rendering Unison file...
+
+  Typechecking Unison file...
+
+  I merged scratch/topic into scratch/main.
+```